In the art the term "scale" has been used inconsistently depending on the particular art which is being considered. For example, the dentist would probably associate the word "scale" with plaque (i.e. organic material) adhered to teeth. On the other hand the detergent chemist would probably associate the term "scale" with "soap scum", that is to say insoluble calcium salts of soaps. However, in the particular cleaning composition art with which the subject invention is concerned, scale means limescale. As used herein limescale means insoluble metal salts, which salts have effectively zero solubility in water. Limescale is usually formed from insoluble salts such as magnesium carbonate, magnesium sulfate, calcium carbonate, calcium sulfate and mixtures thereof.
As is well known in the art, limescale can accumulate as a solid water insoluble deposit in places which come into contact with water, for example around the bases of hot and cold water taps in the bathroom and in the kitchen and inside the toilet bowl. The mentioned deposits once deposited are difficult to remove without damaging the relevant surface, for example the toilet bowl, the taps, the sink, bath or basin.
Difficulties with the depositing of limescale are more likely to occur in hard water areas rather than soft water areas. Hard water contains finely divided quantities of calcium sulphates and carbonates which can react to be deposited as limescale on the relevant surfaces.
Compositions for removing limescale usually act by dissolving away the insoluble limescale stain. Since the resulting solution is usually washed into the domestic drainage system, and from the domestic drainage system through the usual water treatment plants, and ultimately into rivers and into the sea, it is accordingly desirable that acid limescale removing compositions and the salts thereof, whether in solution or out of solution, should be biodegradable.
Many limescale removers are known in the art. Early limescale removers were formulations comprising aqueous hydrochloric acid. Subsequently there were formulations comprising organic acids, said organic acids usually being C.sub.1 -C.sub.5 acids, for example citric acid and maleic acid.
One bathroom cleaner and limescale remover known in the art is sold under the tradename "OzO". It is stated to be ideal for plastic and enamel baths, sinks, taps and tiles.
A good limescale remover will have the following advantages:
1. It will be safe. More specifically, a cleaning composition is likely to come into contact with human skin, and might even come into contact with eyes. Thus, it is important that such skin or eye contact causes minimum discomfort and no lasting damage. PA1 2. It will be fast-acting. Depending on the extent of the limescale stain, it is usually necessary to leave the limescale remover in contact with the stain for a short time. Usually, even with a small degree of staining, limescale removers do not remove the stain instantaneously. Good limescale removers would also be sufficiently viscous such that the composition will remain in contact with the limescale stain, for example around a tap base, rather than running away, but on the other hand, not too viscous such that they cannot be applied evenly and easily. PA1 3. A good limescale remover will ideally be biodegradable as mentioned above. PA1 4. A good limescale will, again as mentioned above, be safe for use in the toilet bowl, on taps and other surfaces without causing damage thereto. It may be necessary to use a limescale remover on such surfaces as porcelain, plastic, enamel, iron, stainless steel and plated surfaces. It is important that the scale remover should not damage any of these substrates, and in particular should not etch enamels or plated surfaces. PA1 R.sup.2 independently can be selected from --CH.sub.2 CO.sub.2 H, alkyl, alkylaryl and --CH(CO.sub.2 H)--(CH.sub.2).sub.p CO.sub.2 H; and EQU R.sup.3 --X--(CH.sub.2).sub.n CO.sub.2 H (2) PA1 X independently can be selected from O and S; PA1 R.sup.3 independently can be selected from --(CH.sub.2).sub.n CO.sub.2 H, --CH(CH.sub.2).sub.m CO.sub.2 H!.sub.2, HO.sub.2 C--CH--CH.sub.2 CO.sub.2 H, and --CH(CO.sub.2 H)--(CH.sub.2).sub.p CO.sub.2 H PA1 i) iminodiacetic acid; PA1 ii) aspartic acid; PA1 iii) derivatives selected from N-alkyl, N-alkylaryl and N-cycloaliphatic derivatives of iminodiacetic acid; PA1 iv) derivatives selected from N-alkyl, N-alkylaryl and N-cycloaliphatic derivatives of aspartic acid; and PA1 v) C.sub.2 -C.sub.10 polycarboxylic acids, PA1 i) iminodiacetic acid; PA1 ii) aspartic acid; PA1 iii) derivatives selected from N-alkyl, N-alkylaryl and N-cycloaliphatic derivatives of iminodiacetic acid; PA1 iv) derivatives selected from N-alkyl, N-alkylaryl and N-cycloaliphatic derivatives of aspartic acid; and PA1 v) certain C.sub.2 -C.sub.10 polycarboxylic acids. PA1 vi) acids having either general formula (1) or general formula (2): ##STR2## wherein: R.sup.1 independently can be selected from H, alkyl, alkylaryl, --(CH.sub.2).sub.n CO.sub.2 H, --CH((CH.sub.2).sub.m CO.sub.2 H).sub.2 and --CH(CO.sub.2 H)--(CH.sub.2).sub.p COOH; PA1 R.sup.2 independently can be selected from --CH.sub.2 CO.sub.2 H, alkyl, alkylaryl and --CH(CO.sub.2 H)--(CH.sub.2).sub.p CO.sub.2 H; and EQU R.sup.3 --X--(CH.sub.2).sub.n CO.sub.2 H (2) PA1 X independently can be selected from O and S; PA1 R.sup.3 independently can be selected from --(CH.sub.2).sub.n CO.sub.2 H, --CH(CH.sub.2).sub.m CO.sub.2 H!.sub.2, HO.sub.2 C--CH--CH.sub.2 CO.sub.2 H, and --CH(CO.sub.2 H)--(CH.sub.2).sub.p CO.sub.2 H PA1 H and alkyl: H; C.sub.1 to C.sub.10 PA1 alkyl aryl: C.sub.6 to C.sub.14 PA1 cycloaliphatic: alkylcyclohexyl or alkylcyclopentyl with alkyl range of C.sub.5 to C.sub.14. PA1 i) said acid in an amount of 1 weight percent to 15 weight percent; PA1 ii) said enzyme wherein each enzyme is present in an amount of 0.1 weight percent to 4 weight percent; PA1 iii) said thickener in an amount of 0.2 weight percent to 6 weight percent; PA1 iv) said surfactant in an amount of 0.05 weight percent to 10 weight percent; PA1 v) said cobuilder in an amount of 0.5 weight percent to 12 weight percent; PA1 vi) effective amounts of ingredients selected from sequestering agents, dyes, bleaches, bleach activators, foam control agents and fragrances; and PA1 vii) balance water.
The compositions of the subject invention have all the advantages listed under paragraphs 1-4 above, and furthermore are preferably at least twice as efficient, or more preferably five times as efficient as similar compositions comprising citric acid while maintaining a very similar pH to the citric acid composition. If the composition is too acidic, then the composition is likely to be less safe. The efficiency of the various compositions for cleaning is determined in accordance with the "marble cube test", details of which are set out below.